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深海地殼存在「吃碳」微生物

2010年11月25日
摘譯自2010年11月22日ENS美國,俄勒岡州科,瓦利斯報導;洪美惠編譯;蔡麗伶審校

科學家在深海地殼發現吃碳氫化合物和天然氣的微生物,他們具有天生儲存碳的潛力。

隨著大氣中的溫室氣體二氧化碳含量增加,海洋中二氧化碳濃度也跟著上升,使得海水變酸妨害到珊瑚礁的健康。人類原本就有將二氧化碳打入深海,嘗試將其永久封存其中的想法。而來自俄勒岡州立大學的研究,意味著深海地殼在二氧化碳封存的角色上又多了一樣。

該校海洋暨大氣科學系教授菲斯克(Martin Fisk)指出,「這是個幾乎沒有人研究過的新的生態系統,我們原本預期會發現一些細菌型態,卻沒料到會發現到一大串在地球深處的生物活動,著實令人吃驚。」報告中也提到,這廣淼海底下的微生物分解作用,「對海洋和大氣的生物地球化學(biogeochemistry)方面,具有顯著影響的潛力」。

深海海底地殼涵蓋70%全球地表面積,人類已經探索其地質,但對其生物學領域卻毫無所悉。探索深海地殼非常困難而且昂貴,大部分研究人員早已假設在這種極端的壓力和接近水沸點的高溫環境下,應該沒甚麼生物活動發生。

在中大西洋海底的亞特蘭蒂斯地塊,俄勒岡州的研究人員發現一種微生物聚落,可以分解碳氫化合物並固定碳和氮。圖片來自:俄勒岡州立大學。但在大西洋的亞特蘭蒂斯地塊(Atlantis Massif)這座海底山脈,俄勒岡州立大學科學家鑽探岩層深入超過4600英尺,發現到很深很古老的岩層,並發現到範圍廣泛的生物活動跡象。

這些微生物會分解碳氫化合物,有些細菌似乎能夠氧化甲烷,並擁有活化的固碳基因,或是將氣體分解成氮和碳。

沉積層和岩石的溫度隨海洋深度而增加,科學家現在相信,生物能存活的最高溫度約在250度。

海洋地底一般由三層組成,一是淺層沉積層,二是由岩漿固化的玄武岩層(basalt),第三是更深層冷卻較慢的岩漿所形成的玄武岩,被稱為輝長岩層(gabbro layer),是形成海洋地殼的主要形式。

輝長岩層在地殼下2英里處。但因為地殼上升和斷層作用,造成亞特蘭蒂斯地塊露出,因此研究人員能夠取得輝長岩層形成的核心樣本,並得以調查這些岩石的微生物學現象。

這個深海地殼生物活動的研究,19日發表在「PLoS One」期刊。

研究人員還指出,火星上的甲烷可能源自地質,並結論出,火星地表環境產生的甲烷,可能如同此研究發現那樣,可以提供細菌生存機會。

這項研究由美國國家科學基金會(National Science Foundation)、美國能源部(U.S. Department of Energy)、戈登和貝蒂摩爾基金會(Gordon and Betty Moore Foundation)和綜合大洋鑽探計劃(Integrated Ocean Drilling Program) 所支助。

Carbon-eating Microbes Discovered Deep in Oceanic Crust
CORVALLIS, Oregon, November 22, 2010 (ENS)

Deep in the Earth's oceanic crust, scientists have found bacteria that can eat hydrocarbons and natural gas, and have the genetic potential to store carbon.

Increasing levels of carbon dioxide, a greenhouse gas when in the atmosphere, also raise the levels of carbon dioxide in the oceans, making sea water too acidic to support healthy reefs.

Now, the findings by researchers from Oregon State University reveal a possible role for the deep ocean crust in carbon dioxide storage and fixation by pumping carbon dioxide into deep subsea layers where it might be sequestered permanently.

"This is a new ecosystem that almost no one has ever explored," said Martin Fisk, a professor in the College of Oceanic and Atmospheric Sciences at Oregon State University. "We expected some bacterial forms, but the long list of biological functions that are taking place so deep beneath the Earth is surprising."

Microbial processes in this expansive subseafloor environment "have the potential to significantly influence the biogeochemistry of the ocean and the atmosphere," the researchers wrote in their report.

Oceanic crust covers about 70 percent of the Earth's surface and its geology has been explored, but practically nothing is known about its biology. Exploration is difficult and expensive, and most researchers had assumed little was happening under such extreme conditions of pressure and temperatures near the boiling point of water.

But at a site in the Atlantic Ocean near an undersea mountain, the Atlantis Massif, scientists from Oregon State University drilled more than 4,600 feet into rock that was both very deep and very old, and found a wide range of biological activity.

Microbes were degrading hydrocarbons, some appeared to be capable of oxidizing methane, and there were genes active in the process of fixing, or converting from a gas, both nitrogen and carbon.

The temperature of the sediments and rock increases with depth, and scientists now believe that the upper temperature at which life can exist is around 250 degrees.

The ocean floor is generally composed of three levels - a shallow layer of sediment; basalt formed from solidified magma; and an even deeper level of basalt that cooled more slowly and is called the gabbro layer, which forms the majority of ocean crust.

The gabbro layer begins under a two mile thick layer of crust. But on the Atlantis Massif, core samples were obtained from gabbro rock formations that were closer to the surface than usual because they had been uplifted and exposed by faulting. This allowed the researchers to investigate for the first time the microbiology of these rocks.

Their study of the first exploration of biological activity in the deepest layer of ocean crust was published Friday in the journal "PLoS One."

The researchers also noted that methane found on Mars could be derived from geological sources, and concluded that subsurface environments on Mars where methane is produced could support bacteria like those found in this study.

The research was supported by the National Science Foundation, U.S. Department of Energy, Gordon and Betty Moore Foundation, and the Integrated Ocean Drilling Program.

全文及圖片詳見:ENS報導

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蔡麗伶(LiLing Barricman)

In my healing journey and learning to attain the breath awareness, I become aware of the reality that all the creatures of the world are breathing the same breath. Take action, here and now. From my physical being to the every corner of this out of balance's planet.